Spacers for finfets (field effect transistors)

ABSTRACT

A spacer structure for FinFETs. The structure includes (a) a substrate, (b) a semiconductor fin region on top of the substrate, (c) a gate dielectric region on side walls of the semiconductor fin region, and (d) a gate electrode region on top and on side walls of the semiconductor fin region. The gate dielectric region (i) is sandwiched between and (ii) electrically insulates the gate electrode region and the semiconductor fin region. The structure further includes a first spacer region on a first side wall of the gate electrode region. A first side wall of the semiconductor fin region is exposed to a surrounding ambient. A top surface of the first spacer region is coplanar with a top surface of the gate electrode region.

This application is a divisional application claiming priority to Ser. No. 11/679,862, filed Feb. 28, 2007.

FIELD OF THE INVENTION

The present invention relates generally to spacers for FETs (Field Effect Transistors) and more particularly to the formation of spacers for FinFETs.

BACKGROUND OF THE INVENTION

In a conventional fabrication process of a FinFET (Fin Field Effect Transistor), it is desirable to form spacers on side walls of the gate electrode region of the FinFET while keeping the side walls of the fin region exposed to the surrounding ambient. Therefore, there is a need for a method for forming spacers on side walls of the gate electrode region while keeping the side walls of the fin region exposed to the surrounding ambient.

SUMMARY OF THE INVENTION

The present invention provides a structure fabrication method, comprising providing a structure which includes (a) a substrate, (b) a device block on top of the substrate, and (c) a conformal spacer layer on top of both the substrate and the device block, wherein the device block comprises a first side wall and a second side wall, and wherein the first side wall is not parallel to the second side wall; bombarding the conformal spacer layer with particles in directions parallel to the first side wall but not parallel to the second side wall resulting in (i) damaged regions of the conformal spacer layer on the second side wall and (ii) undamaged regions of the conformal spacer layer on the first side wall; and then removing the damaged regions of the conformal spacer layer from the second side wall without removing the undamaged regions of the conformal spacer layer from the first side wall.

The present invention provides a method for forming spacers on side walls of the gate electrode region while keeping the side walls of the fin region exposed to the surrounding ambient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F show a fabrication process for forming a first semiconductor structure, in accordance with embodiments of the present invention.

FIGS. 2A-2C show a fabrication process for forming a second semiconductor structure, in accordance with embodiments of the present invention.

FIGS. 3A-3F show a fabrication process for forming a third semiconductor structure, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1A-1F show a fabrication process for forming a first semiconductor structure 100, in accordance with embodiments of the present invention. More specifically, with reference to FIG. 1A, the fabrication process for forming the first semiconductor structure 100 starts with an SOI (Silicon-On-Insulator) substrate 110+120+130. The SOI substrate 110+120+130 comprises a silicon layer 110, a silicon dioxide layer 120 on top of the silicon layer 110, and a silicon layer 130 on top of the silicon dioxide layer 120.

Next, with reference to FIG. 1B, in one embodiment, a hard mask layer 140 is formed on top of the SOI substrate 110+120+130. More specifically, the hard mask layer 140 can comprise silicon nitride. The hard mask layer 140 can be formed by CVD (Chemical Vapor Deposition) of silicon nitride on top of the SOI substrate 110+120+130.

Next, in one embodiment, the hard mask layer 140 and the silicon layer 130 are patterned resulting in a hard mask region 140′ and a fin region 130′, respectively, as shown in FIG. 1C. More specifically, the hard mask layer 140 and the silicon layer 130 can be patterned using lithographic and etching processes.

Next, with reference to FIG. 1C, in one embodiment, gate dielectric layers (not shown) are formed on side walls 132′ of the fin region 130′. The gate dielectric layers can comprise silicon dioxide. The gate dielectric layers can be formed by thermally oxidizing exposed surfaces of the fin region 130′. It should be noted that, in FIGS. 1C through 1F, the gate dielectric layers are not shown for simplicity.

Next, with reference to FIG. 1D, in one embodiment, a gate electrode region 150 is formed on top of the semiconductor structure 100 of FIG. 1C. The gate electrode region 150 can comprise poly-silicon. The gate electrode region 150 can be formed by (i) depositing a poly-silicon layer (not shown) on top of the semiconductor structure 100 of FIG. 1C and (ii) patterning the deposited poly-silicon layer using lithographic and etching processes resulting in the gate electrode region 150 of FIG. 1D. In one embodiment, the fin region 130′ runs in a direction 131, whereas the gate electrode region 150 runs in a direction 151, wherein the direction 131 is perpendicular to the direction 151.

Next, with reference to FIG. 1E, in one embodiment, a spacer layer 160 is formed on top of the semiconductor structure 100 of FIG. 1D. More specifically, the spacer layer 160 can comprise silicon nitride. The spacer layer 160 can be formed by CVD of silicon nitride on top of the semiconductor structure 100 of FIG. 1D. FIG. 1Ei shows a top-down view of the semiconductor structure 100 of FIG. 1E, whereas FIG. 1Eii shows a cross-section view of the semiconductor structure 100 of FIG. 1E along a plane defined by a line 1Eii-1Eii.

Next, with reference to FIGS. 1E, 1Ei, and 1Eii, the spacer layer 160 is bombarded with ions in directions defined by arrows 170 a and 170 b. The directions 170 a and 170 b (i) are parallel to the side walls 152 (FIG. 1D) of the gate electrode region 150 and (ii) make an angle of 45° with the top surface 122 of the silicon dioxide layer 120. In one embodiment, the spacer layer 160 is bombarded with argon ions. More specifically, the argon ions are accelerated in an electric field (not shown) such that the ion penetration depth 164 is equal to a thickness 162 of the spacer layer 160 times square root of two. It should be noted that the ion bombardment should not penetrate the gate electrode region 150 and the fin region 130′. As a result, only spacer regions of the spacer layer 160 that are on side walls of the gate electrode region 150 and the fin region 130′ that are parallel to the directions 170 a and 170 b are not damaged (undamaged) by the bombarding ions. These undamaged regions are shown in FIG. 1F as spacer regions 164 a, 164 b, 162 a, and 162 b.

Next, in one embodiment, the damaged spacer regions of the spacer layer 160 are removed resulting in the semiconductor structure 100 of FIG. 1F. The damaged spacer regions can be removed by anisotropic etching. The anisotropic etching is selective to the undamaged spacer regions 164 a, 164 b, 162 a, and 162 b of the spacer layer 160 resulting in the undamaged spacer regions 164 a, 164 b, 162 a, and 162 b remaining on side walls of the gate electrode region 150 and the fin region 130′. It should be noted that the top surfaces of the undamaged spacer regions 162 a and 162 b are coplanar with the top surface 156 of the gate electrode region 150. In an alternative embodiment, the damaged spacer regions of the spacer layer 160 are isotropically etched selectively to the undamaged spacer regions 164 a, 164 b, 162 a, and 162 b of the spacer layer 160. As a result of inevitable over etching, the removal of the damaged spacer regions also results in the removal of the gate dielectric layers beneath the damaged spacer regions.

Next, in one embodiment, conventional steps can be performed on the semiconductor structure 100 of FIG. 1F to form a transistor (not shown). More specifically, extension and halo regions (not shown) are formed in the fin region 130′ using ion implantation. Next, second spacer regions (not shown) are formed on side walls of the spacer regions 162 a and 162 b, and no spacer is formed on side walls 132′ of the fin region 130′. The second spacer regions can be formed in a manner similar to the manner in which the spacer regions 162 a and 162 b are formed on the side walls 152 (FIG. 1D) of the gate electrode region 150. Next, source/drain regions (not shown) are formed in the fin region 130′. The source/drain regions can be formed by ion implantation in the directions 170 a and 170 b.

In summary, after the removal the damaged spacer regions of the spacer layer 160, the undamaged spacer regions 162 a and 162 b of the spacer layer 160 remain on side walls 152 (FIG. 1D) of the gate electrode region 150, whereas the side walls 132′ of the fin region 130′ are exposed to the surrounding ambient. In other words, the spacer regions 162 a and 162 b are formed on side walls 152 of the gate electrode region 150, and no spacer is formed on side walls 132′ of the fin region 130′. After that, conventional steps can be performed on the semiconductor structure 100 of FIG. 1F to form a transistor.

FIGS. 2A-2C show a fabrication process for forming a second semiconductor structure 200, in accordance with embodiments of the present invention. More specifically, the fabrication process for forming the second semiconductor structure 200 starts with the semiconductor structure 200 of FIG. 2A, wherein the semiconductor structure 200 of FIG. 2A is similar to the semiconductor structure 100 of FIG. 1E. The formation of the semiconductor structure 200 of FIG. 2A is similar to the formation of the semiconductor structure 100 of FIG. 1E.

Next, in one embodiment, the spacer layer 160 is anisotropically etched (e.g., using dry etching) resulting in a spacer region 262 on side walls of (i) the gate electrode region 150, (ii) the fin region 130′, and (iii) the hard mask region 140′ as shown in FIG. 2B. FIG. 2Bi shows a top-down view of the semiconductor structure 200 of FIG. 2B, whereas FIG. 2Bii shows a cross-section view of the semiconductor structure 200 of FIG. 2B along a plane defined by a line 2Bii-2Bii.

Next, with reference to FIGS. 2B, 2Bi, and 2Bii, the spacer region 262 is bombarded with ions in directions defined by arrows 270 a and 270 b. The directions 270 a and 270 b (i) are parallel to side walls 152 (FIG. 1D) of the gate electrode region 150 and (ii) make an angle of 45° with the top surface 122 of the silicon dioxide layer 120. In one embodiment, the spacer region 262 is bombarded with argon ions. More specifically, the argon ions are accelerated in an electric field (not shown) such that the ion penetration depth 264′ is equal to a thickness 262′ of the spacer region 262 times square root of two. It should be noted that the ion bombardment should not penetrate the gate electrode region 150 and the fin region 130′. As a result, only regions of the spacer region 262 that are on side walls of the gate electrode region 150 and the fin region 130′ that are parallel to the directions 270 a and 270 b are not damaged (undamaged) by the bombarding ions. These undamaged spacer regions are shown in FIG. 2C as spacer regions 264 a, 264 b, 266 a, and 266 b.

Next, in one embodiment, the damaged regions of the spacer region 262 are removed resulting in the semiconductor structure 200 of FIG. 2C. The damaged spacer regions can be removed by anisotropic (vertical) etching. The anisotropic etching is selective to the undamaged spacer regions of the spacer region 262 resulting in the semiconductor structure 200 of FIG. 2C. As a result of inevitable over etching, the removal of the damaged spacer regions also results in the removal of the gate dielectric layers beneath the damaged spacer regions. Alternatively an isotropic etch can be used to selectively remove the damaged portions of the spacer.

Next, in one embodiment, conventional steps can be performed on the semiconductor structure 200 of FIG. 2C to form a transistor (not shown). More specifically, extension and halo regions (not shown) are formed in the fin region 130′ using ion implantation. Next, second spacer regions (not shown) are formed on side walls of the spacer regions 264 a and 264 b, and no spacer is formed on side walls 132′ of the fin region 130′. The second spacer regions can be formed in a manner similar to the manner in which the spacer regions 264 a and 264 b are formed on the side walls 152 of the gate electrode region 150. Next, source/drain regions (not shown) are formed in the fin region 130′. The source/drain regions can be formed by ion implantation in the directions 270 a and 270 b.

In summary, after the removal the damaged regions of the spacer region 262, the undamaged spacer regions 264 a and 264 b of the spacer region 262 remain on side walls 152 (FIG. 1D) of the gate electrode region 150, whereas the side walls 132′ of the fin region 130′ are exposed to the surrounding ambient. In other words, the spacer regions 264 a and 264 b are formed on side walls 152 of the gate electrode region 150, and no spacer is formed on side walls 132′ of the fin region 130′. After that, conventional steps can be performed on the semiconductor structure 200 of FIG. 2C to form a transistor.

FIGS. 3A-3F show a fabrication process for forming a third semiconductor structure 400, in accordance with embodiments of the present invention. More specifically, the fabrication process for forming the third semiconductor structure 400 starts with the semiconductor structure 400 of FIG. 3A, wherein the semiconductor structure 400 of FIG. 3A is similar to the semiconductor structure 100 of FIG. 1D. The formation of the semiconductor structure 400 of FIG. 3A is similar to the formation of the semiconductor structure 100 of FIG. 1D.

Next, with reference to FIG. 3B, in one embodiment, a first spacer layer 460 is formed on top of the semiconductor structure 400 of FIG. 3A. More specifically, the first spacer layer 460 can comprise silicon nitride. The first spacer layer 460 can be formed by CVD of silicon nitride on top of the semiconductor structure 400 of FIG. 3A.

Next, with reference to FIG. 3C, in one embodiment, a second spacer layer 480 is formed on top of the first spacer layer 460 such that the thickness of the first spacer layer 460 is greater than the thickness of the second spacer layer 480. More specifically, the second spacer layer 480 can comprise silicon dioxide. The second spacer layer 480 can be formed by CVD of silicon dioxide on top of the first spacer layer 460. FIG. 3Ci shows a top-down view of the semiconductor structure 400 of FIG. 3C, whereas FIG. 3Cii shows a cross-section view of the semiconductor structure 400 of FIG. 3C along a plane defined by a line 3Cii-3Cii.

Next, with reference to FIGS. 3C, 3Ci, and 3Cii, the second spacer layer 480 is bombarded with ions in directions defined by arrows 470 a and 470 b. The directions 470 a and 470 b (i) are parallel to the side walls 152 of the gate electrode region 150 and (ii) make an angle of 45° with the top surface 122 of the silicon dioxide layer 120. In one embodiment, the second spacer layer 480 is bombarded with argon ions. More specifically, the argon ions are accelerated in an electric field (not shown) such that the ion penetration depth is equal to a thickness of the second spacer layer 480 times square root of two. It should be noted that the ion bombardment should not penetrate the gate electrode region 150 and the fin region 130′. As a result, only regions of the second spacer layer 480 that are on planes that are parallel to the directions 470 a and 470 b (i.e., on the planes that are parallel to the side walls 152 of the gate electrode region 150) are not damaged (undamaged) by the bombarding ions. These undamaged spacer regions are shown in FIG. 3D as spacer regions 484 a, 484 b, 482 a, and 482 b. It can be considered that (i) the spacer regions 482 a and 482 b are on side walls 152 of the gate electrode region 150 and (ii) the damaged spacer regions of the second spacer layer 480 are on side walls 132′ of the fin region 130′.

Next, in one embodiment, the damaged spacer regions of the second spacer layer 480 are removed resulting in the semiconductor structure 400 of FIG. 3D. The damaged spacer regions can be removed by isotropic etching. The isotropic etching is selective to (i) the undamaged spacer regions 484 a, 484 b, 482 a, and 482 b of the second spacer layer 480 and (ii) the first spacer layer 460.

Next, in one embodiment, the first spacer region 460 is isotropically etched until the side walls 132′ (FIG. 3E) of the fin region 130′ are exposed to the surrounding ambient resulting in the semiconductor structure 400 of FIG. 3E. The isotropic etching is selective to the spacer regions 484 a, 484 b, 482 a, and 482 b. As a result, after the isotropic etching of the first spacer region 460, spacer regions 462 a and 462 b of the first spacer region 460 (shown in FIG. 3F) remain on side walls of the gate electrode region 150, and no spacer remains on side walls 132′ of the fin region 130′.

Next, with reference to FIG. 3E, in one embodiment, the spacer regions 484 a, 484 b, 482 a, and 482 b are removed resulting in the semiconductor structure 400 of FIG. 3F. The spacer regions 484 a, 484 b, 482 a, and 482 b can be removed by isotropic etching. The isotropic etching is selective to spacer regions 462 a, 462 b, 464 a, and 464 b (shown in FIG. 3F).

Next, in one embodiment, conventional steps can be performed on the semiconductor structure 400 of FIG. 3F to form a transistor (not shown). More specifically, extension and halo regions (not shown) are formed in the fin region 130′ using ion implantation. Next, second spacer regions (not shown) are formed on side walls of the spacer regions 462 a and 462 b, and no spacer is formed on side walls 132′ of the fin region 130′. The second spacer regions can be formed in a manner similar to the manner in which the spacer regions 462 a and 462 b are formed on the side walls 152 of the gate electrode region 150. Next, source/drain regions (not shown) are formed in the fin region 130′. The source/drain regions can be formed by ion implantation in the directions 470 a and 470 b.

In summary, after the removal of the spacer regions 484 a, 484 b, 482 a, and 482 b, the spacer regions 462 a, 462 b, 464 a, and 464 b remain on side walls 152 of the gate electrode region 150, whereas the side walls 132′ of the fin region 130′ are exposed to the surrounding ambient. In other words, the spacer regions 462 a and 462 b are formed on side walls of the gate electrode region 150, and no spacer is formed on side walls 132′ of the fin region 130′.

While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention. 

1. A structure, comprising: (a) a substrate; (b) a semiconductor fin region on top of the substrate; (c) a gate dielectric region on side walls of the semiconductor fin region; (d) a gate electrode region on top walls and on said side walls of the semiconductor fin region, wherein the gate dielectric region (i) is sandwiched between and (ii) electrically insulates the gate electrode region and the semiconductor fin region; and (e) a spacer layer on top of the substrate, the semiconductor fin region, and the gate electrode region, wherein the spacer layer comprises (i) a damaged region on side walls of the semiconductor fin region and (ii) an undamaged region on side walls of the gate electrode region, and wherein the damaged region comprises a material which is not present in (i) the undamaged region, (ii) the semiconductor fin region, and (iii) the gate electrode region.
 2. The structure of claim 1, wherein the spacer layer comprises silicon nitride.
 3. A structure, comprising: (a) a substrate which includes a top substrate surface; (b) a semiconductor fin region on top of the top substrate surface; (c) a gate dielectric region on side walls of the semiconductor fin region; (d) a gate electrode region on top walls and on said side walls of the semiconductor fin region, wherein the gate dielectric region (i) is sandwiched between and (ii) electrically insulates the gate electrode region and the semiconductor fin region; and (e) a first spacer region on a first side wall of the gate electrode region, wherein a first side wall of the semiconductor fin region is exposed to a surrounding ambient, and wherein a top surface of the first spacer region is coplanar with a top surface of the gate electrode region.
 4. The structure of claim 3, further comprising a second spacer region on a second side wall of the gate electrode region such that the gate electrode region is sandwiched between the first spacer region and the second spacer region, wherein a second side wall of the semiconductor fin region is exposed to a surrounding ambient, and wherein a top surface of the second spacer region is coplanar with the top surface of the gate electrode region.
 5. The structure of claim 3, further comprising a third spacer region on a first side wall of the first spacer region such that the first spacer region is sandwiched between the third spacer region and the gate electrode region.
 6. The structure of claim 5, wherein a top surface of the third spacer region is farther away from the top substrate surface than the top surface of the first spacer region.
 7. The structure of claim 5, wherein the first spacer region comprises a first dielectric spacer material, wherein the third spacer region comprises a second dielectric spacer material, and wherein the first dielectric spacer material is different from the second dielectric spacer material. 